diff --git a/src/celengine/body.cpp b/src/celengine/body.cpp
index 51192afff9..e5dfec8d36 100644
--- a/src/celengine/body.cpp
+++ b/src/celengine/body.cpp
@@ -813,7 +813,7 @@ bool Body::extant(double t) const
 }
 
 
-void Body::getLifespan(double& begin, double& end) const
+void Body::getLifespan(std::optional<double>& begin, std::optional<double>& end) const
 {
     begin = timeline->startTime();
     end = timeline->endTime();
diff --git a/src/celengine/body.h b/src/celengine/body.h
index 27686ff9a5..dd3925ba61 100644
--- a/src/celengine/body.h
+++ b/src/celengine/body.h
@@ -308,8 +308,7 @@ class Body
     Eigen::Vector3d eclipticToPlanetocentric(const Eigen::Vector3d& ecl, double tdb) const;
 
     bool extant(double) const;
-    void setLifespan(double, double);
-    void getLifespan(double&, double&) const;
+    void getLifespan(std::optional<double>&, std::optional<double>&) const;
 
     Surface* getAlternateSurface(const std::string&) const;
     void addAlternateSurface(const std::string&, Surface*);
diff --git a/src/celengine/fisheyeprojectionmode.cpp b/src/celengine/fisheyeprojectionmode.cpp
index 782d5e5e72..c9753eb652 100644
--- a/src/celengine/fisheyeprojectionmode.cpp
+++ b/src/celengine/fisheyeprojectionmode.cpp
@@ -59,7 +59,7 @@ float FisheyeProjectionMode::getFieldCorrection(float /*zoom*/) const
 }
 
 celmath::Frustum
-FisheyeProjectionMode::getFrustum(float nearZ, float farZ, float zoom) const
+FisheyeProjectionMode::getFrustum(float nearZ, std::optional<float> farZ, float zoom) const
 {
     return celmath::Frustum(getFOV(zoom), width / height, nearZ, farZ);
 }
diff --git a/src/celengine/fisheyeprojectionmode.h b/src/celengine/fisheyeprojectionmode.h
index cb3453ca6a..505c53ca0e 100644
--- a/src/celengine/fisheyeprojectionmode.h
+++ b/src/celengine/fisheyeprojectionmode.h
@@ -32,7 +32,7 @@ class FisheyeProjectionMode : public ProjectionMode
     float getZoom(float fov) const override;
     float getPixelSize(float zoom) const override;
     float getFieldCorrection(float zoom) const override;
-    celmath::Frustum getFrustum(float nearZ, float farZ, float zoom) const override;
+    celmath::Frustum getFrustum(float nearZ, std::optional<float> farZ, float zoom) const override;
     double getViewConeAngleMax(float zoom) const override;
 
     float getNormalizedDeviceZ(float nearZ, float farZ, float z) const override;
diff --git a/src/celengine/parseobject.cpp b/src/celengine/parseobject.cpp
index f23f8453f1..ce5f22f4cd 100644
--- a/src/celengine/parseobject.cpp
+++ b/src/celengine/parseobject.cpp
@@ -87,27 +87,31 @@ GetDefaultUnits(bool usePlanetUnits, double& distanceScale)
 bool
 ParseDate(const Hash* hash, const string& name, double& jd)
 {
-    // Check first for a number value representing a Julian date
-    if (auto jdVal = hash->getNumber<double>(name); jdVal.has_value())
+    if (auto value = ParseDate(hash, name); value.has_value())
     {
-        jd = *jdVal;
+        jd = value.value();
         return true;
     }
+    return false;
+}
+
+std::optional<double>
+ParseDate(const Hash* hash, const string& name)
+{
+    // Check first for a number value representing a Julian date
+    if (auto jdVal = hash->getNumber<double>(name); jdVal.has_value())
+        return *jdVal;
 
     if (const std::string* dateString = hash->getString(name); dateString != nullptr)
     {
         astro::Date date(1, 1, 1);
         if (astro::parseDate(*dateString, date))
-        {
-            jd = (double) date;
-            return true;
-        }
+            return static_cast<double>(date);
     }
 
-    return false;
+    return std::nullopt;
 }
 
-
 /*!
  * Create a new Keplerian orbit from an ssc property table:
  *
diff --git a/src/celengine/parseobject.h b/src/celengine/parseobject.h
index 56fa86f263..05bb5ed9ad 100644
--- a/src/celengine/parseobject.h
+++ b/src/celengine/parseobject.h
@@ -14,6 +14,7 @@
 
 #include <string>
 #include <memory>
+#include <optional>
 #include <celephem/orbit.h>
 #include <celephem/rotation.h>
 #include <celcompat/filesystem.h>
@@ -34,6 +35,7 @@ enum class DataDisposition
 
 
 bool ParseDate(const Hash* hash, const std::string& name, double& jd);
+std::optional<double> ParseDate(const Hash* hash, const std::string& name);
 
 celestia::ephem::Orbit* CreateOrbit(const Selection& centralObject,
                                     const Hash* planetData,
diff --git a/src/celengine/perspectiveprojectionmode.cpp b/src/celengine/perspectiveprojectionmode.cpp
index bf344077ad..9534dfba2c 100644
--- a/src/celengine/perspectiveprojectionmode.cpp
+++ b/src/celengine/perspectiveprojectionmode.cpp
@@ -56,7 +56,7 @@ float PerspectiveProjectionMode::getFieldCorrection(float zoom) const
 }
 
 celmath::Frustum
-PerspectiveProjectionMode::getFrustum(float nearZ, float farZ, float zoom) const
+PerspectiveProjectionMode::getFrustum(float nearZ, std::optional<float> farZ, float zoom) const
 {
     return celmath::Frustum(getFOV(zoom), width / height, nearZ, farZ);
 }
diff --git a/src/celengine/perspectiveprojectionmode.h b/src/celengine/perspectiveprojectionmode.h
index 8013d9ab29..3176ae8723 100644
--- a/src/celengine/perspectiveprojectionmode.h
+++ b/src/celengine/perspectiveprojectionmode.h
@@ -32,7 +32,7 @@ class PerspectiveProjectionMode : public ProjectionMode
     float getZoom(float fov) const override;
     float getPixelSize(float zoom) const override;
     float getFieldCorrection(float zoom) const override;
-    celmath::Frustum getFrustum(float nearZ, float farZ, float zoom) const override;
+    celmath::Frustum getFrustum(float nearZ, std::optional<float> farZ, float zoom) const override;
     double getViewConeAngleMax(float zoom) const override;
 
     float getNormalizedDeviceZ(float nearZ, float farZ, float z) const override;
diff --git a/src/celengine/projectionmode.h b/src/celengine/projectionmode.h
index 950ee6eaac..ac6d4502fa 100644
--- a/src/celengine/projectionmode.h
+++ b/src/celengine/projectionmode.h
@@ -10,6 +10,7 @@
 #pragma once
 
 #include <Eigen/Core>
+#include <optional>
 
 class ShaderManager;
 
@@ -36,7 +37,7 @@ class ProjectionMode
     virtual float getZoom(float fov) const = 0;
     virtual float getPixelSize(float zoom) const = 0;
     virtual float getFieldCorrection(float zoom) const = 0;
-    virtual celmath::Frustum getFrustum(float nearZ, float farZ, float zoom) const = 0;
+    virtual celmath::Frustum getFrustum(float nearZ, std::optional<float> farZ, float zoom) const = 0;
 
     // Calculate the cosine of half the maximum field of view. We'll use this for
     // fast testing of object visibility.
diff --git a/src/celengine/render.cpp b/src/celengine/render.cpp
index c0cbe2e66e..fd1a8a635f 100644
--- a/src/celengine/render.cpp
+++ b/src/celengine/render.cpp
@@ -1531,7 +1531,7 @@ void Renderer::draw(const Observer& observer,
     m_cameraOrientation = Quaterniond(m_cameraTransform) * observer.getOrientation();
 
     // Get the view frustum used for culling in camera space.
-    auto frustum = projectionMode->getFrustum(MinNearPlaneDistance, std::numeric_limits<float>::infinity(), zoom);
+    auto frustum = projectionMode->getFrustum(MinNearPlaneDistance, std::nullopt, zoom);
 
     // Get the transformed frustum, used for culling in the astrocentric coordinate
     // system.
@@ -3939,7 +3939,7 @@ void Renderer::renderDeepSkyObjects(const Universe& universe,
     dsoRenderer.renderFlags      = renderFlags;
     dsoRenderer.labelMode        = labelMode;
 
-    dsoRenderer.frustum = projectionMode->getFrustum(MinNearPlaneDistance, std::numeric_limits<float>::infinity(), observer.getZoom());
+    dsoRenderer.frustum = projectionMode->getFrustum(MinNearPlaneDistance, std::nullopt, observer.getZoom());
     // Use pixelSize * screenDpi instead of FoV, to eliminate windowHeight dependence.
     // = 1.0 at startup
     float effDistanceToScreen = mmToInches((float) REF_DISTANCE_TO_SCREEN) * pixelSize * getScreenDpi();
diff --git a/src/celengine/solarsys.cpp b/src/celengine/solarsys.cpp
index 49283ae976..e7f1170c64 100644
--- a/src/celengine/solarsys.cpp
+++ b/src/celengine/solarsys.cpp
@@ -272,24 +272,30 @@ TimelinePhase::SharedConstPtr CreateTimelinePhase(Body* body,
                                                   const ReferenceFrame::SharedConstPtr& defaultBodyFrame,
                                                   bool isFirstPhase,
                                                   bool isLastPhase,
-                                                  double previousPhaseEnd)
+                                                  std::optional<double> previousPhaseEnd)
 {
-    double beginning = previousPhaseEnd;
-    double ending = std::numeric_limits<double>::infinity();
+    std::optional<double> beginning = previousPhaseEnd;
+    std::optional<double> ending = std::nullopt;
 
     // Beginning is optional for the first phase of a timeline, and not
     // allowed for the other phases, where beginning is always the ending
     // of the previous phase.
-    bool hasBeginning = ParseDate(phaseData, "Beginning", beginning);
-    if (!isFirstPhase && hasBeginning)
+    if (auto newBeginning = ParseDate(phaseData, "Beginning"); newBeginning.has_value())
     {
-        GetLogger()->error("Error: Beginning can only be specified for initial phase of timeline.\n");
-        return nullptr;
+        beginning = newBeginning.value();
+        if (!isFirstPhase)
+        {
+            GetLogger()->error("Error: Beginning can only be specified for initial phase of timeline.\n");
+            return nullptr;
+        }
     }
 
     // Ending is required for all phases except for the final one.
-    bool hasEnding = ParseDate(phaseData, "Ending", ending);
-    if (!isLastPhase && !hasEnding)
+    if (auto newEnding = ParseDate(phaseData, "Ending"); newEnding.has_value())
+    {
+        ending = newEnding.value();
+    }
+    else if (!isLastPhase)
     {
         GetLogger()->error("Error: Ending is required for all timeline phases other than the final one.\n");
         return nullptr;
@@ -375,7 +381,7 @@ Timeline* CreateTimelineFromArray(Body* body,
                                   const ReferenceFrame::SharedConstPtr& defaultBodyFrame)
 {
     auto timeline = std::make_unique<Timeline>();
-    double previousEnding = -std::numeric_limits<double>::infinity();
+    std::optional<double> previousEnding = std::nullopt;
 
     if (timelineArray->empty())
     {
@@ -487,8 +493,8 @@ bool CreateTimeline(Body* body,
     ReferenceFrame::SharedConstPtr bodyFrame;
     celestia::ephem::Orbit* orbit = nullptr;
     celestia::ephem::RotationModel* rotationModel  = nullptr;
-    double beginning  = -std::numeric_limits<double>::infinity();
-    double ending     =  std::numeric_limits<double>::infinity();
+    std::optional<double> beginning  = std::nullopt;
+    std::optional<double> ending     = std::nullopt;
 
     // If any new timeline values are specified, we need to overrideOldTimeline will
     // be set to true.
@@ -601,10 +607,16 @@ bool CreateTimeline(Body* body,
         rotationModel = CreateDefaultRotationModel(syncRotationPeriod);
     }
 
-    if (ParseDate(planetData, "Beginning", beginning))
+    if (auto newBeginning = ParseDate(planetData, "Beginning"); newBeginning.has_value())
+    {
+        beginning = newBeginning.value();
         overrideOldTimeline = true;
-    if (ParseDate(planetData, "Ending", ending))
+    }
+    if (auto newEnding = ParseDate(planetData, "Ending"); newEnding.has_value())
+    {
+        ending = newEnding.value();
         overrideOldTimeline = true;
+    }
 
     // Something went wrong if the disposition isn't modify and no timeline
     // is to be created.
@@ -612,7 +624,7 @@ bool CreateTimeline(Body* body,
 
     if (overrideOldTimeline)
     {
-        if (beginning >= ending)
+        if (beginning.has_value() && ending.has_value() && beginning.value() >= ending.value())
         {
             GetLogger()->error("Beginning time must be before Ending time.\n");
             delete rotationModel;
diff --git a/src/celengine/timeline.cpp b/src/celengine/timeline.cpp
index 8dee834bab..aa422e6379 100644
--- a/src/celengine/timeline.cpp
+++ b/src/celengine/timeline.cpp
@@ -40,7 +40,8 @@ Timeline::appendPhase(TimelinePhase::SharedConstPtr &phase)
     // no gaps and no overlaps.
     if (!phases.empty())
     {
-        if (phase->startTime() != phases.back()->endTime())
+        auto startTime = phase->startTime();
+        if (!startTime.has_value() || startTime.value() != phases.back()->endTime())
             return false;
     }
 
@@ -64,7 +65,8 @@ Timeline::findPhase(double t) const
     {
         for (const auto& phase : phases)
         {
-            if (t < phase->endTime())
+            auto endTime = phase->endTime();
+            if (!endTime.has_value() || t < endTime.value())
                 return phase;
         }
 
@@ -92,14 +94,14 @@ Timeline::phaseCount() const
 }
 
 
-double
+std::optional<double>
 Timeline::startTime() const
 {
     return phases.front()->startTime();
 }
 
 
-double
+std::optional<double>
 Timeline::endTime() const
 {
     return phases.back()->endTime();
@@ -114,7 +116,11 @@ Timeline::endTime() const
 bool
 Timeline::includes(double t) const
 {
-    return phases.front()->startTime() <= t && t <= phases.back()->endTime();
+    if (auto startTime = phases.front()->startTime(); startTime.has_value() && t < startTime.value())
+        return false;
+    if (auto endTime = phases.back()->endTime(); endTime.has_value() && t > endTime.value())
+        return false;
+    return true;
 }
 
 
diff --git a/src/celengine/timeline.h b/src/celengine/timeline.h
index 6fb32dc339..261aaf22a4 100644
--- a/src/celengine/timeline.h
+++ b/src/celengine/timeline.h
@@ -13,6 +13,7 @@
 #pragma once
 
 #include <memory>
+#include <optional>
 #include <vector>
 #include "timelinephase.h"
 
@@ -27,8 +28,8 @@ class Timeline
     const TimelinePhase::SharedConstPtr& getPhase(unsigned int n) const;
     unsigned int phaseCount() const;
 
-    double startTime() const;
-    double endTime() const;
+    std::optional<double> startTime() const;
+    std::optional<double> endTime() const;
     bool includes(double t) const;
 
     void markChanged();
diff --git a/src/celengine/timelinephase.cpp b/src/celengine/timelinephase.cpp
index c6c3d84c56..d456e434e2 100644
--- a/src/celengine/timelinephase.cpp
+++ b/src/celengine/timelinephase.cpp
@@ -23,8 +23,8 @@
 using namespace std;
 
 TimelinePhase::TimelinePhase(Body* _body,
-                             double _startTime,
-                             double _endTime,
+                             std::optional<double> _startTime,
+                             std::optional<double> _endTime,
                              const ReferenceFrame::SharedConstPtr& _orbitFrame,
                              celestia::ephem::Orbit* _orbit,
                              const ReferenceFrame::SharedConstPtr& _bodyFrame,
@@ -47,15 +47,15 @@ TimelinePhase::TimelinePhase(Body* _body,
 TimelinePhase::SharedConstPtr
 TimelinePhase::CreateTimelinePhase(Universe& universe,
                                    Body* body,
-                                   double startTime,
-                                   double endTime,
+                                   std::optional<double> startTime,
+                                   std::optional<double> endTime,
                                    const ReferenceFrame::SharedConstPtr& orbitFrame,
                                    celestia::ephem::Orbit& orbit,
                                    const ReferenceFrame::SharedConstPtr& bodyFrame,
                                    celestia::ephem::RotationModel& rotationModel)
 {
     // Validate the time range.
-    if (endTime <= startTime)
+    if (endTime.has_value() && startTime.has_value() && endTime.value() <= startTime.value())
         return nullptr;
 
     // Get the frame tree to add the new phase to. Verify that the reference frame
diff --git a/src/celengine/timelinephase.h b/src/celengine/timelinephase.h
index 0b375d1690..562f7c6509 100644
--- a/src/celengine/timelinephase.h
+++ b/src/celengine/timelinephase.h
@@ -13,6 +13,7 @@
 #pragma once
 
 #include <memory>
+#include <optional>
 #include "frame.h"
 
 class FrameTree;
@@ -36,12 +37,12 @@ class TimelinePhase
         return m_body;
     }
 
-    double startTime() const
+    std::optional<double> startTime() const
     {
         return m_startTime;
     }
 
-    double endTime() const
+    std::optional<double> endTime() const
     {
         return m_endTime;
     }
@@ -79,13 +80,26 @@ class TimelinePhase
      */
     bool includes(double t) const
     {
-        return m_startTime <= t && t < m_endTime;
+        if (m_startTime.has_value() && t < m_startTime.value())
+            return false;
+        if (m_endTime.has_value() && t >= m_endTime.value())
+            return false;
+        return true;
+    }
+
+    double clamp(double t) const
+    {
+        if (m_startTime.has_value() && t < m_startTime.value())
+            return m_startTime.value();
+        if (m_endTime.has_value() && t > m_endTime.value())
+            return m_endTime.value();
+        return t;
     }
 
     static TimelinePhase::SharedConstPtr CreateTimelinePhase(Universe& universe,
                                                              Body* body,
-                                                             double startTime,
-                                                             double endTime,
+                                                             std::optional<double> startTime,
+                                                             std::optional<double> endTime,
                                                              const ReferenceFrame::SharedConstPtr& orbitFrame,
                                                              celestia::ephem::Orbit& orbit,
                                                              const ReferenceFrame::SharedConstPtr& bodyFrame,
@@ -94,8 +108,8 @@ class TimelinePhase
     ~TimelinePhase() = default;
 
     TimelinePhase(Body* _body,
-                  double _startTime,
-                  double _endTime,
+                  std::optional<double> _startTime,
+                  std::optional<double> _endTime,
                   const ReferenceFrame::SharedConstPtr& _orbitFrame,
                   celestia::ephem::Orbit* _orbit,
                   const ReferenceFrame::SharedConstPtr& _bodyFrame,
@@ -108,8 +122,8 @@ class TimelinePhase
 private:
     Body* m_body;
 
-    double m_startTime;
-    double m_endTime;
+    std::optional<double> m_startTime;
+    std::optional<double> m_endTime;
 
     ReferenceFrame::SharedConstPtr m_orbitFrame;
     celestia::ephem::Orbit* m_orbit;
diff --git a/src/celestia/qt/qtinfopanel.cpp b/src/celestia/qt/qtinfopanel.cpp
index 2e688d63d9..63f7ed1ce8 100644
--- a/src/celestia/qt/qtinfopanel.cpp
+++ b/src/celestia/qt/qtinfopanel.cpp
@@ -226,15 +226,15 @@ void InfoPanel::buildSolarSystemBodyPage(const Body* body,
             stream << QString(_("<b>Has atmosphere</b>")) << "<br>\n";
 
         // Start and end dates
-        double startTime = 0.0;
-        double endTime = 0.0;
+        std::optional<double> startTime = std::nullopt;
+        std::optional<double> endTime = std::nullopt;
         body->getLifespan(startTime, endTime);
 
-        if (startTime > -1.0e9)
-            stream << "<br>" << QString(_("<b>Start:</b> %1")).arg(astro::TDBtoUTC(startTime).toCStr()) << "<br>\n";
+        if (startTime.has_value())
+            stream << "<br>" << QString(_("<b>Start:</b> %1")).arg(astro::TDBtoUTC(startTime.value()).toCStr()) << "<br>\n";
 
-        if (endTime < 1.0e9)
-            stream << "<br>" << QString(_("<b>End:</b> %1")).arg(astro::TDBtoUTC(endTime).toCStr()) << "<br>\n";
+        if (endTime.has_value())
+            stream << "<br>" << QString(_("<b>End:</b> %1")).arg(astro::TDBtoUTC(endTime.value()).toCStr()) << "<br>\n";
 
         stream << "<br><big><b>" << QString(_("Orbit information")) << "</b></big><br>\n";
         stream << QString(_("Osculating elements for %1")).arg(astro::TDBtoUTC(t).toCStr()) << "<br>\n";
diff --git a/src/celestia/qt/qtselectionpopup.cpp b/src/celestia/qt/qtselectionpopup.cpp
index a6cfb60cf5..7ce4eb63a1 100644
--- a/src/celestia/qt/qtselectionpopup.cpp
+++ b/src/celestia/qt/qtselectionpopup.cpp
@@ -65,26 +65,26 @@ SelectionPopup::SelectionPopup(const Selection& sel,
         addAction(boldTextItem(QString::fromStdString(sel.body()->getName(true))));
 
         // Start and end dates
-        double startTime = 0.0;
-        double endTime = 0.0;
+        std::optional<double> startTime = std::nullopt;
+        std::optional<double> endTime = std::nullopt;
         sel.body()->getLifespan(startTime, endTime);
 
-        if (startTime > -1.0e9 || endTime < 1.0e9)
+        if (startTime.has_value() || endTime.has_value())
         {
             addSeparator();
 
-            if (startTime > -1.0e9)
+            if (startTime.has_value())
             {
-                QString startDateStr = QString(_("Start: %1")).arg(astro::TDBtoUTC(startTime).toCStr());
+                QString startDateStr = QString(_("Start: %1")).arg(astro::TDBtoUTC(startTime.value()).toCStr());
                 QAction* startDateAct = new QAction(startDateStr, this);
                 connect(startDateAct, SIGNAL(triggered()),
                         this, SLOT(slotGotoStartDate()));
                 addAction(startDateAct);
             }
 
-            if (endTime < 1.0e9)
+            if (endTime.has_value())
             {
-                QString endDateStr = QString(_("End: %1")).arg(astro::TDBtoUTC(endTime).toCStr());
+                QString endDateStr = QString(_("End: %1")).arg(astro::TDBtoUTC(endTime.value()).toCStr());
                 QAction* endDateAct = new QAction(endDateStr, this);
                 connect(endDateAct, SIGNAL(triggered()),
                         this, SLOT(slotGotoEndDate()));
@@ -646,20 +646,22 @@ void SelectionPopup::slotToggleTerminator()
 void SelectionPopup::slotGotoStartDate()
 {
     assert(selection.body() != nullptr);
-    double startDate = 0.0;
-    double endDate = 0.0;
+    std::optional<double> startDate = std::nullopt;
+    std::optional<double> endDate = std::nullopt;
     selection.body()->getLifespan(startDate, endDate);
-    appCore->getSimulation()->setTime(startDate);
+    if (startDate.has_value())
+        appCore->getSimulation()->setTime(startDate.value());
 }
 
 
 void SelectionPopup::slotGotoEndDate()
 {
     assert(selection.body() != nullptr);
-    double startDate = 0.0;
-    double endDate = 0.0;
+    std::optional<double> startDate = std::nullopt;
+    std::optional<double> endDate = std::nullopt;
     selection.body()->getLifespan(startDate, endDate);
-    appCore->getSimulation()->setTime(endDate);
+    if (endDate.has_value())
+        appCore->getSimulation()->setTime(endDate.value());
 }
 
 
diff --git a/src/celmath/frustum.cpp b/src/celmath/frustum.cpp
index fe5a742bf3..df35f71ed4 100644
--- a/src/celmath/frustum.cpp
+++ b/src/celmath/frustum.cpp
@@ -23,16 +23,16 @@ Frustum::Frustum(float fov, float aspectRatio, float n) :
     init(fov, aspectRatio, n, n);
 }
 
-Frustum::Frustum(float fov, float aspectRatio, float n, float f) :
-    infinite(std::isinf(f))
+Frustum::Frustum(float fov, float aspectRatio, float n, std::optional<float> f) :
+    infinite(!f.has_value())
 {
-    init(fov, aspectRatio, n, infinite ? n : f);
+    init(fov, aspectRatio, n, infinite ? n : f.value());
 }
 
-Frustum::Frustum(float l, float r, float t, float b, float n, float f) :
-    infinite(std::isinf(f))
+Frustum::Frustum(float l, float r, float t, float b, float n, std::optional<float> f) :
+    infinite(!f.has_value())
 {
-    init(l, r, t, b, n, infinite ? n : f);
+    init(l, r, t, b, n, infinite ? n : f.value());
 }
 
 void Frustum::init(float fov, float aspectRatio, float n, float f)
diff --git a/src/celmath/frustum.h b/src/celmath/frustum.h
index e379f404d2..939ef34f3d 100644
--- a/src/celmath/frustum.h
+++ b/src/celmath/frustum.h
@@ -12,6 +12,7 @@
 #include <Eigen/Core>
 #include <Eigen/Geometry>
 
+#include <optional>
 
 namespace celmath
 {
@@ -22,8 +23,8 @@ class Frustum
     using PlaneType = Eigen::Hyperplane<float, 3>;
 
     Frustum(float fov, float aspectRatio, float nearDist);
-    Frustum(float fov, float aspectRatio, float nearDist, float farDist);
-    Frustum(float left, float right, float top, float bottom, float nearDist, float farDist);
+    Frustum(float fov, float aspectRatio, float nearDist, std::optional<float> farDist);
+    Frustum(float left, float right, float top, float bottom, float nearDist, std::optional<float> farDist);
 
     inline Eigen::Hyperplane<float, 3> plane(unsigned int which) const
     {
diff --git a/src/celscript/lua/celx_object.cpp b/src/celscript/lua/celx_object.cpp
index 40f057bdf8..f7ece01b52 100644
--- a/src/celscript/lua/celx_object.cpp
+++ b/src/celscript/lua/celx_object.cpp
@@ -670,10 +670,11 @@ static int object_getinfo(lua_State* l)
         float eqRadius = max(semiAxes.x(), semiAxes.z());
         celx.setTable("oblateness", (eqRadius - polarRadius) / eqRadius);
 
-        double lifespanStart, lifespanEnd;
+        std::optional<double> lifespanStart;
+        std::optional<double> lifespanEnd;
         body->getLifespan(lifespanStart, lifespanEnd);
-        celx.setTable("lifespanStart", (lua_Number)lifespanStart);
-        celx.setTable("lifespanEnd", (lua_Number)lifespanEnd);
+        celx.setTable("lifespanStart", static_cast<lua_Number>(lifespanStart.value_or(-std::numeric_limits<double>::infinity())));
+        celx.setTable("lifespanEnd", static_cast<lua_Number>(lifespanEnd.value_or(std::numeric_limits<double>::infinity())));
         // TODO: atmosphere, surfaces ?
 
         PlanetarySystem* system = body->getSystem();
diff --git a/src/celscript/lua/celx_phase.cpp b/src/celscript/lua/celx_phase.cpp
index 46254503cd..7feb861ec5 100644
--- a/src/celscript/lua/celx_phase.cpp
+++ b/src/celscript/lua/celx_phase.cpp
@@ -76,7 +76,7 @@ static int phase_timespan(lua_State* l)
     celx.checkArgs(1, 1, "No arguments allowed for to phase:timespan");
 
     auto phase = this_phase(l);
-    celx.push(phase->startTime(), phase->endTime());
+    celx.push(phase->startTime().value_or(-std::numeric_limits<double>::infinity()), phase->endTime().value_or(std::numeric_limits<double>::infinity()));
     //lua_pushnumber(l, phase->startTime());
     //lua_pushnumber(l, phase->endTime());
 
@@ -135,10 +135,7 @@ static int phase_getposition(lua_State* l)
     auto phase = this_phase(l);
 
     double tdb = celx.safeGetNumber(2, WrongType, "Argument to phase:getposition() must be number", 0.0);
-    if (tdb < phase->startTime())
-        tdb = phase->startTime();
-    else if (tdb > phase->endTime())
-        tdb = phase->endTime();
+    tdb = phase->clamp(tdb);
     celx.newPosition(UniversalCoord(phase->orbit()->positionAtTime(tdb) * astro::kilometersToMicroLightYears(1.0)));
 
     return 1;
@@ -160,10 +157,7 @@ static int phase_getorientation(lua_State* l)
     auto phase = this_phase(l);
 
     double tdb = celx.safeGetNumber(2, WrongType, "Argument to phase:getorientation() must be number", 0.0);
-    if (tdb < phase->startTime())
-        tdb = phase->startTime();
-    else if (tdb > phase->endTime())
-        tdb = phase->endTime();
+    tdb = phase->clamp(tdb);
     celx.newRotation(phase->rotationModel()->orientationAtTime(tdb));
 
     return 1;